Transfection of cells, whether in vitro, ex vivo or in vivo, involves not only delivery of the transfecting DNA to the cell nucleus, but also expression of the delivered DNA in the cell. Some gene delivery systems involve transfection of cells using a delivery complex in which DNA is condensed with cationic polymers such as cationic lipids or polylysine (see, for example, Cotten and Wagner (1993) Curr. Opin. Biotech., 4: 705). There is a need in the art for a gene delivery system which is stable in the bloodstream, targetable to selected tissue types, and capable of efficient transport into the cytoplasm and to the nucleus of both dividing and non-dividing cells. Some transfection techniques demonstrate that the transfecting DNA may be absorbed by cells, only to accumulate unchanged in the cytoplasm and unexpressed in the nucleus (for example, see Zaubner et al., (1995) J. Biol. Chem. 270: 18997, wherein cationic liposomes carrying DNA accumulate in the cytoplasm), suggesting that there is a need in the art for improvements in current methods of cell transfection.